1. Field of the Invention:
This invention relates generally to bicycle brake assemblies. It more particularly relates to an adjustable shoe mounting structure for a bicycle brake assembly.
2. Description of the Prior Art:
As is well known, most commonly used for bicycles available in the market are so-called caliper brakes. This type of brake includes a pair of brake arms or calipers pivotally supported on the bicycle frame (front fork or rear fork) to be positioned on both sides of a wheel, each caliper being provided at its lower end with a brake shoe in facing relation to the wheel rim. Upon actuation of a remote brake lever, the calipers are pivoted in a braking direction, so that the brake shoes come into braking contact with the rim.
Obviously, when brake shoes are positioned or oriented improperly relative to a wheel rim, it becomes difficult to obtain a good braking performance, which may put the rider in danger during cycling. However, there are various types of bicycles which may differ from each other in various points such as brake mounting position, and front or rear fork inclination. Thus, when using the same type of brakes for different types of bicycles, it is necessary to properly adjust the shoe position and/or orientation relative to the wheel rim depending on the particular bicycle type. Further, even in the case of a single bicycle, it is periodically necessary to readjust the shoe position to compensate for shoe abrasion after repeated use of the brake.
In view of such a requirement, it is quite common to mount brake shoes by means of adjustable mounting structures.
A typical shoe mounting structure for a prior art brake comprises a bolt reception bore penetrating through a shoe support portion of a brake arm lengthwise of the bicycle, and a support bolt loosely inserted through the bolt reception bore. The support bolt has a threaded end projecting from one end of the bolt reception bore for engagement with a nut, and an enlarged end or head projecting from the other end of the bore. The bolt head is formed with a cross bore extending transversely of the bolt. The brake shoe has a mounting pin inserted into the bolt cross bore.
With the shoe mounting structure described above, when the nut is tightened up, the mounting pin of the brake shoe is pressed transversely against the bolt cross bore, thereby fixing the shoe relative to the brake arm. On the other hand, when the nut is loosened, the support bolt and the shoe mounting pin become loose for adjusting movement or rotation. For example, the shoe mounting pin may be slidably moved relative to the bolt cross bore for horizontal adjustment toward or away from the wheel rim, the mounting pin being further rotatable within the bolt cross bore for orientation adjustment. Moreover, the support bolt may be rotated within the bolt reception bore for second orientation adjustment. If necessary, the bolt reception bore may be elongated vertically in cross-section to provide vertical adjustment of the shoe position.
In this way, the prior art shoe mounting structure provides at least three degrees, preferably four or more degrees, of adjusting freedom. Thus, by utilizing such diversity in the adjusting freedom, it is possible to bring the shoe to an optimum position (orientation) relative to the wheel rim in each particular type of bicycle.
However, such diversity in the adjusting freedom can often result in difficulty of adjusting operation. In fact, it is not always necessary to adjust the shoe position in every direction or degree of adjusting freedom. For example, if the horizontal position and angular orientation of the shoe are already proper, only the vertical position of the shoe need be adjusted by vertically moving the support bolt within the vertically elongated reception bore. Nevertheless, both of the support bolt and the shoe mounting pin inevitably become loose upon slackening the nut, which may cause unexpected movement and/or rotation of the shoe mounting pin to come out of previously proper position and/or orientation. In an extreme case, it may become necessary to readjust the shoe position and/or orientation in every degree of the adjusting freedom from the very start.
Thus, according to the prior art shoe mounting structure, the diversity in the adjusting freedom, though enabling a wide range of adjustment, can often give rise to a problem of making the adjusting operation troublesome and time-taking.
In view of the above disadvantage of the typical prior art shoe mounting structure, Japanese Utility Model Publication No. 55-47740 (Published: Nov. 8, 1980; Application No.: 51-161890; Filed: Dec. 2, 1976; Inventor: Yohsuke FUKUI; Applicant: Shimano Industrial Co., Ltd.) proposes an improvement in a shoe mounting structure which is similar in basic arrangement to the typical prior art discussed above. Specifically, the improvement comprises a cam plate mounted on the support bolt and interposed between the shoe support portion of a brake arm and the mounting pin of the brake shoe. The cam plate is urged into pressing contact with the shoe mounting pin by a compression coil spring which is accommodated in a recess of the shoe support portion.
According to the arrangement proposed by the Japanese utility model publication, the compression spring urges the cam plate in pressing contact with the shoe mounting pin even upon loosening the nut for positional adjustment. As a result, the shoe mounting pin is always pressed transversely against the cross bore of the support bolt, thereby frictionally restraining the movement of the shoe mounting pin relative to the support bolt during positional adjustment of the brake shoe. On the other hand, the shoe mounting pin may be forcibly moved and/or rotated within the cross bore of the support bolt if a sufficient manual force is applied to overcome the friction imparted by the compression spring. Thus, it is possible to facilitate the adjusting operation while enjoying the benefits of the diverse adjusting freedom.
However, the cam plate of the above Japanese utility model is pressed against the shoe mounting pin merely by the urging force of the compression spring. Therefore, the cam plate may move away from the shoe mounting pin if an operator's finger accidentally comes into contact with the cam plate during the adjusting operation, thereby bringing the shoe mounting pin into its loose state relative to the support cross bore. This state gives rise to the same problem as already described in connection with the typical prior art.